The use of an interventional apparatus such as a microcatheter assembly for placing occlusive devices, such as embolic coils, stents and dilation balloons, at target sites throughout the body have become standard procedures for endovascular disease treatment. Such approach is particularly useful in treating diseases that are located where traditional operational procedures pose a greater risk to the patient. Examples of these devices and their applications are shown in U.S. Pat. Nos. 5,261,916, 5,354,295 and 6,958,068, in which different methods of delivery and deployment of devices to sites, such as aneurysms are disclosed.
Embolic Coils such as those discussed in the above-mentioned documents are generally made of a radiopaque, biocompatible material typically metal such as platinum, tungsten, nitinol or alloys of these and other metals.
In treating peripheral or neural diseases such as aneurysm, typically, the procedures involve inserting a microcatheter over a guidewire into the vasculature and to a predetermined target site. Following the insertion of the microcatheter, an occlusive device, such as an embolic coil, attached at the distal end of a delivery assembly is then inserted through the lumen of the microcatheter towards the target site. Once the position of occlusive device at the target site is confirmed through radiological technique, the occlusive device is then detached from the delivery assembly to leave the occlusive device positioned at the target site. The detachment of the occlusive device is of utmost importance. Despite the technological advancement in the field of delivering occlusive devices to a target site, there are still problems associated with many of the current techniques. These problems include the ease of positioning and repositioning the occlusive coil before detachment, the accuracy in positioning the occlusive coil at the target site, and the duration of the deployment procedure.
In order to address the above-mentioned concerns, several different techniques are developed regarding the release mechanism of the occlusive device. Electrolytic detachment of an occlusive coil from a delivery wire is disclosed in U.S. Pat. Nos. 5,122,136 and 5,354,295. A metal occlusive coil is bonded to a dissimilar metal at the distal end of the delivery wire. Once the occlusive coil is deployed at the desired location, a small electrical current is passed through the guidewire and the occlusive coil will be detached via electrolysis. One advantage to this method is an improved accuracy of positioning the occlusive coil compared to detachment by mechanical force. However, several drawbacks make this technique less than optimal. One drawback is the need for accessories such as a power supply and electrical cables. Another drawback is that this is a time consuming technique because of the additional time required before the electrolysis reaction has sufficiently detached the occlusive coil. Furthermore, because of the electrical current, patients may experience discomfort during the electrolysis process.
An electrical resistance heating coil detachment procedure is disclosed in U.S. Pat. No. 6,478,773. The occlusive coil is mounted to the distal portion of the delivery assembly by a tubular collar that uses and electrical resistance coil that when heated will expand the collar and release the occlusive coil. This releasing procedure is similar to the electrolytic technique, discussed above, and similarly has the advantage of a highly accurate occlusive coil placement. Drawbacks again include the need for power supply accessories and the additional time required for the heat conduction to occur and the coil to be detached.
Hydraulic deployment is disclosed in U.S. Pat. Nos. 6,361,547 and 6,607,538. The occlusive coil is joined onto the microcatheter and a hydraulic injector or a syringe by attachment to the proximal end of the microcatheter. The occlusive coil can be released from the microcatheter when a fluid pressure as high as 300 pound per square inch (300 psi) is supplied through a lumen of the catheter, forcing the distal tip of the catheter to expand outward and in turn releasing the occlusive coil. The advantage of this method is the rapid detachment of the coil once the positioning of the coil is done. The drawback of this technique is the high hydraulic force introduced into the aneurysm which may led to potential rupture of the aneurysm.
Mechanical locking system between the coil and the delivery assembly is another type of deployment method which avoids the need for additional accessories during coil deployment. There are several types of interlocking mechanism for releasing an occlusive coil. Examples of such methods and apparatuses can be found in U.S. Pat. Nos. 5,261,916, 5,304,195, 5,350,397, 6,458,137 and 7,344,558.
One interlocking mechanism for embolic coil deployment is disclosed in U.S. Pat. No. 5,261,916. The pusher-embolic coil assembly has an interlocking ball and keyway coupling which can be manipulated in order to release the occlusive coil. Another similar mechanism is outlined in U.S. Pat. No. 5,304,195. The pusher-occlusive coil assembly of this patent has an interlocking ball and ball coupling which can be manipulated in order to release the occlusive coil. In another similar mechanism described in U.S. Pat. No. 5,350,397, the occlusive coil has an enlarged member such as a ball attached. The occlusive coil can be released by forcing the enlarge member through an aperture in a socket situated on the distal end of a pusher assembly. The device also include a plunger which is situated within the pusher housing which is use to force the occlusive coil out of the socket at the distal end of the assembly. The plunger can be activated axially or a screw driven device in which a knob can be rotated to push the ball out of the aperture of the socket and hence releasing the occlusive coil. The above-mentioned interlocking designs may all encounter similar drawback of the over-extension of the delivery assembly into the aneurysm causing damage to the wall of the aneurysm which may in turn led to further intracranial hemorrhage.
Another interlocking mechanism for occlusive coil deployment is disclosed in U.S. Pat. No. 6,458,137. The assembly comprises a delivery wire and the occlusive coil is attached onto the wire through thread and screw mechanism. The occlusive coil can be detached from the wire by rotating the wire so to unscrew the coil from the delivery wire. The drawback of this technique is the difficulty of rotating a long and thin delivery wire at the proximal end in order to release the occlusive coil at the distal end of the device.
Yet another interlocking mechanism for occlusive coil deployment is disclosed in U.S. Pat. No. 7,344,558. The delivery assembly includes a plunger which has a constrictor located at its distal end. The constrictor has a reduced size which grasps the occlusive coil. When the coil is ready to be deployed, the constrictor is rotated in an opposite direction to increase its size which in turn released the coil. Both U.S. Pat. Nos. 6,458,137 and 7,344,558 have similar rotating release mechanism which would encounter similar drawback of transferring the torque force from the proximal end to the distal end of the delivery assembly through the tortuous narrow neurovascular system.
The above discussion showed that even though various deployment methods are available, each and every method in the art has one or more of a variety of drawbacks. Therefore, a controlled, rapid and reliable deployment method for embolic coil without the need of external electrical power supply and the risk of further hemorrhage is needed in the art.